Abstract: This paper presents results of simulations for a case of heavy rain that occurred in May 1994 over South China using the fifth generation Penn State/NCAR mesoscale model (MM5). The model result recaptures the major observed features of these events as well as the associated mesoscale system. Within a weakly fored synotic scale environment, convective activity was trigged by boundary layer convergence.The hourly precipitation generally increased with the increasing of magnitude of 200 hPa divergence minus 925 hPa convergence,and the occurring time of maximum precipitation rate lagged that of the maximum divergence difference by less than an hour.The secondary circulation induced by latent heat release resulted in the development and maintaining of mesoscale low-level jet and disturebance,then the mesoscale rising motion and precipitation as well as latent heat release were further strengthened.This reaction process is simily to .CISK Therefore the latent heating is a crucial factor in the development and maintaining of this heavy raill process.